1. Field of the Invention
The present invention relates to an air conditioner using a heater, and in particular to an air conditioner which uses a heater provided with heat sources in the inside thereof for heating air to be supplied, and controls air-conditioning so as to keep a room temperature of an air-conditioned room constant.
2. Description of the Related Art
In a clean room (air-conditioned room) used in a semiconductor manufacturing factory or the like, conditions required for working environment tend to be strict. For example, in a precision environment chamber or the like, temperature control in the chamber is required strictly. In particular, in a space where inspection work or the like is actually carried out in the room, highly accurate temperature control is required for an air conditioner, for example, fluctuation of temperature in the space is required to be controlled to ±{fraction (1/1000)}° C. or less.
Japanese Patent Application Publication No. 6-272963 discloses an air conditioner provided with a heater and a cooler for maintaining temperature in a room at a desired temperature in order to meet the requirements. The heater and the cooler are feedback controlled while monitoring a room temperature with a temperature sensor or the like to keep the room temperature constant.
As the heater, a heat transfer wire is used, which has a high electric resistance wound around in a coil shape (or plate shape) as a heat source in an air duct (supply path) of the air conditioner. Heat is generated in the heat transfer wire by energizing the heat transfer wire, and air sent by a blower is brought into contact with the heat transfer wire, whereby heated air of a desired temperature is obtained. As the cooler, a cooling coil is provided, in which chilled fluid such as cooling water or fluorocarbon fluid flows, and air is brought into contact with the cooling coil, whereby cooling air of a desired temperature is obtained. That is, a flow rate of chilled fluid cooled to a predetermined temperature is controlled by a pump and supplied to the cooling coil, and air is brought into contact with the cooling coil to keep the air at a desired temperature.
However, the conventional heater has a disadvantage in that it is poor in quick responsiveness to temperature control because it uses the heat transfer wire and is not suitable for an environment in which highly accurate temperature control is desired. Moreover, since the conventional cooler controls temperature of air by controlling a flow rate of supply of chilled fluid to be supplied to the cooling coil, it is difficult to control a flow rate of chilled fluid with respect to controlled temperature of the air. For example, the cooler is poor in quick responsiveness to a change in temperature due to external factors such as an outflow of air caused by opening and closing of a door of a precision environment chamber and is further unsuitable for controlling temperature with high accuracy.
Further, there is a disadvantage in that quick responsiveness cannot be expected with respect to a change in temperature due to external factors as described above simply by providing a heater or a cooler having a single temperature resolution. Furthermore, there is a disadvantage in that, if a plurality of heaters and coolers are provided excessively, control becomes complicated and costs of equipment increase.